Sliding contacts are used in various applications, including motors and generators. Such contacts often comprise a first, stationary contact and a second, rotating contact that is maintained in sliding engagement with the first contact as the second contact rotates relative to the first contact.
Because sliding contacts make physical contact with each other during use, contact wear can be a problem. This is particularly true when higher currents are passed through the contacts. Due to such wear issues, most sliding contacts comprise a metal contact and a graphite brush that brushes across the surface of the metal. Because graphite has a low coefficient of friction, wear is reduced. Conventional graphite and electrographite brushes are not effective above a current density threshold where ohmic heat losses become unmanageable due to the intrinsic bulk resistivity and thermal transport characteristics of these materials. When a graphite brush achieves high temperature due to excessive current density, the threshold being a function of geometry, composition, and environment, water is desorbed from the brush causing catastrophic wear of the brush resulting in system failure. In contrast, metal on metal sliding contacts can be used to pass much higher currents. Therefore, metal on metal sliding contacts would be preferable if it were not for the above-mentioned wear problems.
In view of the above discussion, it can be appreciated that it would be desirable to have metal on metal sliding contacts that are less susceptible to wear.